2M Install - 5/8 wave on roof rack?

Discussion in 'Communication & Navigation' started by lovetoski, Jun 15, 2016.

  1. lovetoski

    lovetoski SILVER Star

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    I am studying for my ham test. Going well, excited to move to that communication medium. I bought a Yeasu 2900R since it's on sale at HRO for $119 (and free shipping). I've read through a bunch of threads on here and on expo, and the obvious antenna choice is a 1/2 wave larsen whip (150B hw) mounted on the back of the truck, just above the tail-lights. Cable routing is easy, reports are that reception is great.

    I have also read that a 5/8 wave antenna performs better, but requires a ground plane...for example NMO mount on the roof. I have a roof rack, with an expanded steel floor. Does the expanded steel floor function as a ground plane, because if it does I could easily install an NMO mount in the middle of the rack floor, enabling me to run a 5/8 antenna.
     
  2. 1911

    1911 chupacabra

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    Good luck on your test, and good choice for your first radio - the 2900 is bullet-proof and a great 2M radio.

    As far as different wavelength antennas performance, "better" is pretty relative. Since 2M is a line-of-sight band, you will get better range by being as high above the truck (including the roof) as possible. Beyond that, 1/4, 1/2, and 5/8-wave antennas have different radiation angles that may or may not suit the kind of terrain that you live in/drive on. Where you mount a 5/8 or 1/4-wave antenna (front, center of roof, back bumper, etc.) will also have more effect on the radiation pattern than on a 1/2-wave.

    There is some good linked reading along these lines in this recent thread: https://forum.ih8mud.com/threads/ham-antenna-suggestions.922606/
    particularly in post #13 and post #40 (both by Dragos80).

    Mounting the antenna on a roof rack will still give you some or most of the ground plane from the roof, depending on if it is on the very edge of the rack or nearer the center.

    Bottom line (in my experience anyway) is higher is better, and the antenna that tunes up the best (lowest SWR) at the location you decide on is the "best". If you use some version of an NMO mount, then you could borrow different antennas from friends and see which gives the lowest SWR before committing to buy one.
     
    Last edited: Jun 16, 2016
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  3. e9999

    e9999 You want to do what...? Moderator

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    I use a magnet mount on the middle of the roof or roof rack, easy. I think it's a better spot than the rear.
     
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  4. Mrtwooooo

    Mrtwooooo

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    The roof or roof rack should be good. I've got a Larsen dual band 2m/70cm antenna mounted in my front bumper and a Larsen 5/8 wave on the roof. Both use NMO mounts so I can change them up wherever I want. I tried the 5/8 on the front bumper once and realized the performance was not that great. Probably because of the lack of ground plane. Whichever you get, get it tuned. Borrow an SWR meter or even better borrow an antenna analyzer. I had to trim my 5/8 antenna down a bit.. The Larsen should come with a little chart to get you close. The analyzer lets me set a frequency to the middle of the band and get m SWR perfect. I'm able to get great range with my 5/8 in the center of my roof.
     
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  5. lovetoski

    lovetoski SILVER Star

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    Thanks MrT...appreciate the info. Attached is a pic of the floor of the rack I built.



    Re the two antenna's you are using, do you use a splitter like shown in this article?

    Redirect Notice

    Rackpic.JPG
     
  6. Mrtwooooo

    Mrtwooooo

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    yeah. the A/B switch
     
  7. mryanangel

    mryanangel SILVER Star

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    I have the same setup, FT2900 with Larson 150 NMO mounted directly in the middle of the roof. The reception is fantastic, but the problem is. I want to be able to mount a RTT for certain trips.

    Has anyone come up with a solution to this problem? Is there an NMO extension cable that could be used to extend the cable to say the edge of the roof rack for times when the RTT is mounted?

    I would prefer to not have to run another cable and would like to keep the antenna as high as possible.
     
  8. badlander

    badlander

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    I mounted the NMO mount to a stainless steel plate and have mounting points on the center of my roof rack and on the side of the rack, actually in the track of the Foxwing awning.. When I mount the RRT it's just a matter of relocating the plate to the side location. Extra cable gets coiled up and wire tied as needed. Takes 5 min. Easy.
    Don't forget to seal up the bottom of the NMO mount with silicone sealer to protect it from the environment.
     
  9. mryanangel

    mryanangel SILVER Star

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    I now have a RTT but still habrnt figire out a good way to extend the NMO mount out to the edge of the rack. I dont want to just pull the nmo put of my rpof as I will have a big gaping hole. I wpuld thing there shpuld be an nmo to nmo extension that allows you to move tge antenna.
     
  10. LC4LIFE

    LC4LIFE SILVER Star

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    I run a Comet SBB-5 antenna mounted in the middle of my roof and it works fantastic for my radio. I picked a roof mount that has a PL-259 connector so I could extend it to the edge of the rack/roof when needed using this. I have never seen and extension for an NMO.
     
  11. mryanangel

    mryanangel SILVER Star

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    I just found this NMO to PL-259 adapter. Now to figure out the cable / mount and antenna options. Which mount did you use for the endge of the rack? Is 3' long enough to reach the edge of the rack from the center of the roof?
     
  12. LC4LIFE

    LC4LIFE SILVER Star

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    There you go...I knew those were out there but didn't connect the dots. Three feet is just long enough. I would use something like this and just clamp the rack, but remove the CB antenna adapter. If that wont work, I would look at fender mounts for CB antennas. There are tons of little brackets out there that may work for your rack. Here is the antenna I have and I really like it. Comet Sbb-5
     
  13. mryanangel

    mryanangel SILVER Star

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    i think I have now ordered up everything to make it work. I picked up the same antenna that you have with the PL-259 connection. An SO-239 bulk head fitting and that mirror mount you found to mount the antenna. Coupled with a pair of 90 degree SO-239 > PL-259 elbows and a 4' cable (SO-239 > PL-259) running back to the NMO > SO-239 adapter and my problem should be resolved.

    Now that the cable and antenna is all set for dual band...maybe I need to think about replacing he FT-2900 with a dual band radio.

    Thanks for the help mate.
     
  14. LC4LIFE

    LC4LIFE SILVER Star

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    Right on...that sounds like it will work well.
     
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